Several plants contain caffeine, such as the coffee bean, the tea leaf, the cocoa bean (cacao), and even the kola nut used for cola beverages. The amount of caffeine in a prepared beverage depends on the type of plant it is made from, the brewing method, and the grind used. Also, the growing conditions of the individual plants, the soils and climates, can effect the concentration of caffeine contained in the plant. Although much of the caffeine we consume occurs naturally in brewed beverages, a good deal of it is added. For instance, although the kola nut does contain caffeine, most of the caffeine in cola soft drinks is added, using purified caffeine obtained from decaffeinated coffee beans. Still, at least 10 percent of the caffeine in colas, and in pepper flavored soft drinks, is obtained from the cola nuts. This naturally occurring caffeine does not have to be listed on the ingredients label, if no other caffeine is added.

Although the FDA classifies caffeine as GRAS (generally recognized as safe), it actually regulates caffeine under three different sections of the Federal Food, Drug, and Cosmetics Act. In coffee and tea, it is a natural ingredient and since the amount of the caffeine these products contains is not seen to ordinarily injure health, are approved and not subject to any legislation concerning their caffeine content.

When caffeine is used as an additive, it's GRAS status means that manufacturers do not have to prove the safety of caffeine, or seek any type of approval to add caffeine to their product. However, the FDA limits the amount of caffeine that can be added to certain foods.

Caffeine is generally recognized as safe when used in cola-type beverages up to a level of 0.02 percent or 200 parts per million. This means that the maximum amount of caffeine allowed in a 12 ounce carbonated beverage (255mL) is about 72mg.

The following table shows the average caffeine amounts in coffee, tea, and over the counter drugs. Please note that it is difficult to give precise ranges of naturally occurring caffeine content. The caffeine content depends on the amount of water used, the method of brewing, and the type of coffee or tea. For instance, lighter roast coffee has slightly more caffeine than a darker roast, which belies the myth that an espresso has more caffeine than a regular cup of coffee. Also, the longer the coffee is exposed to hot water, the great the amount of caffeine that will be extracted. These values should be taken as a means of comparison between different products rather than as a precise indication of the maximum amount of caffeine that a product may contain. The amounts of naturally occuring caffeine in products such as coffee, tea, and chocolate, are given as an average amount that might be found. Note that in reality, the caffeine content exists within a range and the average amounts are reported based on the known ranges, within reason.